The invention relates to geophysical, geological, and geochemical site characterization, and particularly to site characterization in the context of remediation status determination and/or control programs for hazardous waste sites, pollution (e.g. superfund) sites, and the like. Remediation is required at thousands of government and commercial waste sites covering many hundreds of square miles. Remediation programs require site-characterization prior to remediation, during remediation for monitoring purposes, and after remediation for performance evaluation of new remediation technologies. Site characterization includes, for example, locating point sources of contaminants (buried drums and tanks, waste trenches, pits, waste lagoons, disposal boundaries, etc.), mapping the extent of contaminant or leachate plumes, delineating subsurface geologic features that control pathways for contaminant migration, etc. Current techniques for characterization, monitoring, and performance evaluation for subsurface contamination rely heavily on well-drilling that is risky, slow, costly, and inaccurate. Non-invasive geophysical sensing and remote sensing offer potential for dramatic improvement, but there are no super-sensors for solving all or even most of the characterization problems.
Site characterization provides a surface, subsurface, and supersurface picture of relevant conditions such as contamination, integrity, topography, erosion, etc. that provides the basis for assessing status and, e.g., suitability for exposure to humans. Remediation decisions use site characterization data as an input. Site monitoring of relevant characteristics, such as contamination, can also be conducted during remediation to assess whether remediation is proceeding as planned. Performance evaluation of new remediation technologies can be conducted, for example, in specially-designed tests prior to acceptance of the technologies.
In clean-up scenarios, prior art technology for subsurface characterization, monitoring, and performance-evaluation uses well-drilling to determine the nature and extent of contamination. However, wells puncture natural geological barriers to contaminants and pose the risk of providing additional contaminant pathways. Further, wells can be a health and safety risk to site workers. Well-drilling is also very slow and costly. Tens of wells can cost hundreds of thousands of dollars, and, in some highly contaminated areas, a single well can cost a million dollars. Also, because it is difficult to use well data to characterize contamination between wells, overall characterization may be quite inaccurate.
The use of non-invasive geophysical sensors based on electrical, seismic, gravitational, and magnetic methods, coupled with remote sensing from the air and/or from space offers great potential for site characterization. Non-invasive and remote sensing techniques are by their nature safer, faster, and less costly than invasive techniques. Further, near-continuous lateral coverage can be used to characterize site conditions between point-sources of information, such as well sites, for contamination status determination, thereby improving accuracy.
The difficulty with non-invasive and remote sensing is that no one sensor type provides a complete picture of a site. Consequently, prior art use of such sensors has been limited to forming partial pictures with several sensors and manually combining these pictures with prior site and general knowledge, e.g. geological knowledge, to produce and to interpret a picture. For example, an electrical sensor may detect an underground aqueous contaminant plume, and a seismic sensor may detect an impermeable geological structure. The two pictures can be integrated by persons knowing that the plume must be resting on the geological structure. The validity of the manually-interpreted picture is highly dependent on the skill of the interpreter, and accuracy is difficult to quantify.